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Ignition amplifier test?

T

traub

New member
Can somebody verify some resistance & voltage readings I got on my ignition amplifier? I've replaced/bypassed everything else in the circuit and still no spark. Before I shell out $400, I'd like to get a little better feeling that this thing is "bad"
With the unit on my bench, nothing connected to it I get the following Ohm readings.
Black to Purple = 0
Black to Gray = 3,000
Black to Wht/Grn = 2100
Black to Wht/red = 0

If I put 12v to the Purple, gray to ground, I get 12v on the wht/red and 5v on the wht/grn.
1987 350 Mag SN B605821
 
lets start at the beginning, What you have sounds like TB IV . there are 2 purple wires going to the + side of the coil,1 is system power from the key ,the other is power to the module. there are 2 tan or grey wires going to the neg side. 1 is the tach feed going back into the harness, the other is the neg side of the coil to the module.
Bad tach kills spark, shift interupt can do it also.
If this is a TB IV for a V8, i can supply the readings from my module
 
I'm not sure what TB IV is but the wiring configuration you are describing is exactly what I have. I tried removing the purple from the coil coming from the system/key and put a jumper straight from the battery to the coil. This was to eliminate everything...any bad wires/connections/shift switches etc and give a clean 12v to the coil and still no spark. Also removed the one grey wire, so the only thing connected to the coil was purple and grey from the ignition module, and the 12v jumper from the battery.
If the tack is bad (which I don't think it is... as in it was working when it was put away last fall) the grey is a ground right? So wouldn't removing that grey wire it from the coil as I did eliminate/bypass that possibility?
Very much appreciate the feed back. Thank You.
 
I've replaced/bypassed everything else in the circuit and still no spark.
Click to expand...

Under the rotor is the optic sensor. If it is all rusty it won't send a trigger to the amplifier to create a spark. Did you perform the basic tests for the ignition system? They will tell you what item(s) are defective.

Tests for Thunderbolt Ignition:


W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!


Check the kill switch first!


#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts are present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced.
 
Yes, I did all the basic ignition test. The coil and sensor are new. I'm just suprised there is no way to bench test the ignition amplifier. Thats a lot of money to be just parts swapping.
 
What did the bench test say about the amplifier? The price is why it lasted 23 years. I've seen them new for $300 on eBay. But, that was in December - February which is the best time to buy boat items.
 
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